Anaphylaxis is a serious systemic allergic reaction that is rapid in onset and may cause death . The diagnosis of anaphylaxis during the acute event is based on the clinical presentation and a history of a recent exposure to an offending agent . There are no laboratory tests available in an emergency department or clinic setting to confirm a diagnosis of anaphylaxis in real time. (See "Anaphylaxis: Rapid recognition and treatment".)
Laboratory tests in serum, plasma, and possibly urine obtained during or shortly after the acute event, can, however, help to support the clinical diagnosis of anaphylaxis. These tests can also help identify anaphylaxis in the presence of other disorders that have overlapping clinical presentations, such as severe asthma or myocardial infarction. In addition, these tests may provide evidence for anaphylaxis as a cause of death.
This topic reviews the laboratory tests that can be used to support the clinical diagnosis of anaphylaxis in both adults and children. These tests are different from those that identify sensitization to the inciting allergen, namely measurements of allergen-specific immunoglobulin E (IgE), which are reviewed elsewhere. (See "Overview of skin testing for allergic disease" and "Overview of in vitro allergy tests" and "Anaphylaxis: Confirming the diagnosis and determining the trigger(s)", section on 'Testing for allergen trigger(s)'.)
The principal effector cells of systemic anaphylaxis are mast cells and basophils. The various preformed and newly-generated mediators secreted by these cells cause many of the signs and symptoms of systemic anaphylaxis. The pathophysiology of anaphylaxis is reviewed in detail separately. (See "Pathophysiology of anaphylaxis".)
Two of the most abundant and best-characterized preformed granule mediators released by these cells during anaphylaxis are tryptase and histamine. Elevations in tryptase and histamine can sometimes be detected in blood samples obtained shortly after the onset of symptoms. Also, elevated levels of histamine, histamine metabolites (N-methylhistamine and N-methylimidazole acetic acid), the prostaglandin D2 (PGD2) metabolite, 11-beta-prostaglandin F2-alpha (11-beta-PGF2-alpha), and the leukotriene C4 (LTC4) metabolite, leukotriene E4 (LTE4) can be measured in urine after an anaphylactic event.